William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Catherine Burt Driver, MD

Catherine Burt Driver, MD, is board certified in internal medicine and rheumatology by the American Board of Internal Medicine. Dr. Driver is a member of the American College of Rheumatology. She currently is in active practice in the field of rheumatology in Mission Viejo, Calif., where she is a partner in Mission Internal Medical Group.

What is polymyositis? What is dermatomyositis?

Polymyositis is a disease of muscle featuring inflammation of the muscle fibers. The cause of the disease is not known. It begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles. The muscles affected are typically those closest to the trunk or torso. This results in weakness that can be severe. Polymyositis is a chronic illness featuring progressive muscle weakness with periods of increased symptoms, called flares or relapses, and minimal or no symptoms, known as remissions.

Polymyositis is slightly more common in females. It affects all age groups, although its onset is most common in middle childhood and in the 20s. Polymyositis occurs throughout the world. Polymyositis can be associated with a characteristic skin rash and is then referred to as "dermatomyositis." Dermatomyositis in children is referred to as juvenile dermatomyositis. "Amyopathic dermatomyositis" is the term used to describe people who have skin changes compatible with dermatomyositis but do not have diseased muscle involvement.

Polymyositis & Dermatomyositis Symptom

Weakness

Weakness is a decrease in the strength in one or more muscles. In the strictest sense, the medical definition of weakness refers to loss of muscle strength, and this article is focused upon conditions that can result in a measurable loss of muscle function. Weakness may be generalized or may affect one muscle or muscle group exclusively. Diseases of the neuromuscular system, injuries, metabolic diseases, and toxins can all cause of measurable muscle weakness. Signs and symptoms of weakness can include trouble doing daily tasks, such as grooming or writing or problems with gait and loss of balance.

Polymyositis vs. polymyalgia rheumatica

Polymyositis is an inflammatory, destructive, autoimmune muscle disease, usually with weakness but unusually with pain. Polymyalgia rheumatica is an inflammatory disease of muscle that always causes symmetrically painful muscles. Polymyalgia rheumatica is not destructive to muscles.

What causes polymyositis and dermatomyositis?

To date, no cause of polymyositis has been isolated by scientific researchers. There are indicators of heredity (genetic) susceptibility that can be found in some patients. There is indirect evidence of infection by a virus that has yet to be identified in a muscle disease related to polymyositis that is particularly resistant to treatment, called inclusion body myositis. The pathologist, a physician specialist who interprets the microscope findings of muscle tissue, diagnoses this muscle disease. The muscle tissue in inclusion body myositis displays clear areas within the muscle cells (called vacuoles) when viewed under the magnification of a microscope.

Researchers have found that T-cells of the immune system in some polymyositis or dermatomyositis patients reacted against cytomegalovirus (CMV) and that detectable antibodies against CMV were present. Their conclusion was that there may be subsets of patients who develop their disease, in part, because of infection with this particular virus.

What are signs and symptoms of polymyositis and dermatomyositis?

Weakness of muscles is the most common symptom of polymyositis. The muscles involved usually are those that are closest to the trunk of the body. Both sides of the body are affected. The onset can be gradual or rapid. This results in varying degrees of loss of muscle power and atrophy. The loss of strength can be noticed as difficulty getting up from chairs, walking, climbing stairs, or lifting above the shoulders. Trouble with swallowing and weakness lifting the head from the pillow can occur. Occasionally, the muscles ache and are tender to the touch.

Weakness of the muscles that produce the voice can lead to a weak-sounding voice (dysphonia).

With skin involvement (dermatomyositis), the eyes can be surrounded by a violet discoloration with swelling. There can be scaly reddish discoloration over the knuckles, elbows, and knees (Gottron's sign). There can also be reddish rash on the face, neck, and upper chest. The skin changes can occur with or prior to the development of muscle weakness. Hard lumps of calcium deposits can develop in the fatty layer of the skin, most commonly in childhood dermatomyositis.

Because polymyositis can appear in combination with other illnesses (see related articles on systemic lupus erythematosus, scleroderma, and rheumatoid arthritis), it can also have overlap features with them. These illnesses are discussed elsewhere.

What tests do doctors use to diagnose polymyositis or dermatomyositis?

When a patient first sees the doctor, the recent symptoms especially concerning weakness will be discussed. The condition of many other body areas might be reviewed, for example, the skin, heart, lungs, and joints. An examination will further focus on these and other systems. Various measures of strength might be noted. The characteristic features of polymyositis include weakness of the muscles closest to the trunk of the body, abnormal elevation of muscle enzymes, electromyograph (EMG) findings, magnetic resonance imaging (MRI) findings, and certain abnormalities detected with muscle biopsy.

Blood testing usually (but not always) reveals abnormally high levels of muscle enzymes, CPK or creatinine phosphokinase, aldolase, SGOT, SGPT, and LDH. These enzymes are released into the blood by muscle that is being damaged by inflammation. They can also be used as measures of the activity of the inflammation. Other routine blood and urine tests can also look for internal organ abnormalities. Chest X-rays, mammograms, PAP smears, and other screening tests might be considered. Autoantibodies can often be found in the blood of people with polymyositis. These include antinuclear antibodies (ANAs) and myositis-specific antibodies (such as Jo-1 antibody).

An electromyograph (EMG) and nerve conduction velocity are electrical tests of muscle and nerves that can show abnormal findings typical of polymyositis as well as exclude other nerve-muscle diseases.

Imaging of the muscles using radiology tests, such as magnetic resonance imaging (MRI scanning), can show areas of inflammation of muscle. This sometimes can be used to determine optimal muscle biopsy sites.

A muscle biopsy is used to confirm the presence of muscle inflammation typical only of polymyositis. This is a surgical procedure whereby muscle tissue is removed for analysis by a pathologist, a specialist in examining tissue under a microscope. Muscles often used for biopsy include the quadriceps muscle of the front of the thigh, the biceps muscle of the arm, and the deltoid muscle of the shoulder.

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What types of doctors treat polymyositis and dermatomyositis?

Polymyositis is typically treated by rheumatologists. Others who can be involved in the care of patients with polymyositis include internists, pathologists, dermatologists, radiologists, cardiologists, neurologists, surgeons, and physiatrists.

What is the treatment for polymyositis and dermatomyositis?

Initially, polymyositis is treated with high doses of corticosteroids. Corticosteroids are cortisone medications (such as prednisone and prednisolone). These are medications related to cortisone and can be given by mouth or intravenously. They are given because they can have a powerful effect to decrease the inflammation in the muscles. They usually are required for years, and their continued use will be based on what the doctor finds related to symptoms, examination, and muscle enzyme blood test.

Corticosteroids have many predictable and unpredictable side effects. In high doses, they commonly cause an increase in appetite and weight, puffiness of the face, and easy bruising. They can also cause sweats, facial-hair growth, upset stomach, sensitive emotions, leg swelling, acne, cataracts, osteoporosis, high blood pressure, worsening of diabetes, and increased risk of infection. A rare complication of cortisone medications is severe bone damage (avascular necrosis) which can destroy large joints, such as the hips and shoulders. Further, abruptly stopping corticosteroids can cause flares of the disease and result in other side effects, including nausea, vomiting, and decreased blood pressure.

Corticosteroids do not always adequately improve polymyositis. In these patients, immunosuppressive medications are considered. These medications can be effective by suppressing the immune response that attracts the white blood cells of inflammation to the muscles. Many types are now commonly used and others are still experimental. Methotrexate (Rheumatrex, Trexall) can be taken by mouth or by injection into the body. Azathioprine (Imuran) is an oral drug. Both can cause liver and bone-marrow side effects and require regular blood monitoring. Cyclophosphamide (Cytoxan), chlorambucil (Leukeran), and cyclosporine (Sandimmune) have been used for serious complications of severe disease, such as scarring of the lungs (pulmonary fibrosis). These also can have severe side effects which must be considered with each patient individually. Treatment with intravenous infusion of immunoglobulins (IVIG) has been shown to be effective in severe cases of polymyositis that are resistant to other treatments. Recent research reports indicate that intravenous rituximab (Rituxan) may be helpful in treating resistant disease.

Patients with calcium deposits (calcinosis) from dermatomyositis can sometimes benefit by taking diltiazem (Cardizem) to shrink the size of the calcium deposits. This effect, however, occurs slowly (frequently over years) and is not always effective. The complication of calcium deposits in muscles and soft tissues occurs more frequently in children than adults.

Physical therapy with gradual muscle strengthening is an important part of the treatment of polymyositis. When to begin and the continued degree of exercise and range of motion of extremities is customized for each patient.

Patients can ultimately do well, especially with early medical treatment of disease and disease flares. The disease frequently becomes inactive, and rehabilitation of atrophied muscle becomes a long-term project. Monitoring for signs of cancer, heart, and lung disease are essential. Accordingly, EKG, lung function testing, and X-ray tests are used.

As mentioned above, the related muscle disease called inclusion body myositis is often more resistant to treatment than polymyositis. As scientists better define the specific causes of the different forms of polymyositis, treatment will be more accurately aimed at cure of this disease. Researchers are finding more specific antibodies in patients that may be used to diagnose and define active disease.

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What are home remedies for polymyositis and dermatomyositis?

The best home remedy is to closely monitor the condition with the physician and physical therapist. It is best to not over-exercise early on but gradually increase exercise for optimal results.

What is the prognosis for polymyositis?

The outcome for patients with polymyositis varies. While some have a relatively brief illness followed by remission not requiring subsequent treatment, others develop episodes of remissions and exacerbations requiring more or less treatment.

The presence of Jo-1 antibody, a myositis antibody, is predictive of an increased risk for the development of inflammation of the tissues of the lungs (interstitial lung disease). This can lead to permanent suboptimal lung function. Pulmonary function testing can be used to detect early lung abnormalities.

What are risk factors for worse outcomes with polymyositis
or dermatomyositis?

Patients with polymyositis tend to have a higher risk for worse outcomes with older age, delay in cortisone treatment, cancer, lung or heart disease, or difficulty swallowing.

Cancer screening is performed, especially in patients with dermatomyositis, due to an increased risk of cancer in patients with muscle inflammation.

Is it possible to prevent polymyositis?

There is no prevention for polymyositis. When the precise cause of polymyositis is identified, preventative measures might be possible.